The present invention relates to an apparatus and method for removing dissolved oxygen from aqueous fluids on a continuous basis.
It is well known that the presence of oxygen in continuous fluid processes, as well as the products produced thereby, can cause a great deal of detrimental damage. For example, beverages and food product's produced by on-line bottling or canning processes, such as fruit juices, soft drinks, beer, wine, milk, soups, vegetable juices, and pastes, etc. may be unstable over even a relatively short period of time due to undesirable changes produced by oxidative deterioration. In this regard, among the oxidative changes which beverages and food products incur over time include changes in color, consistency, and flavor. Since these changes in the beverages and food products greatly decrease the product's marketability, it is desirable to reduce the presence of oxygen in the overall product.
Furthermore, if oxygen is present in the beverage and/or food product during bottling or canning, the oxygen included in the product can also cause deterioration of the container's plastic or metal lining, packaging, etc. Thus, in modern beverage and food product preparation systems, it is desirable to remove the extraneous oxygen from the fluids to greatly increase the shelf life of the packaged product prior to and/or during on-line processing.
This is particularly important in modern brewing operations, wherein the feed stock must be almost completely deoxygenated in that the presence of even a small fraction of oxygen can result in an unacceptable product. As a result, in modern beverage and food product operations, various deoxygenating devices including vacuum systems, oxygen-purging apparatuses, etc. are used to extract the oxygen.
Along this line, vacuum deareators have been commercially available for some time and have been used to lower the oxygen level in liquid products. Similarly, beverages and food stuffs have also been subject to gas-flushing. However, vacuum deareators and gas flushing apparatuses are fairly expensive and they do not necessarily reduce the dissolve oxygen content to an acceptable level. Furthermore, these apparatuses have some drawbacks in that the oils and lubricants used therein sometimes find their way into the fluids being treated. The inclusion of even a small amount of such harmful agents within the beverage and/or food product can produce undesirable color and/or flavor changes in the overall product, as well as toxic effects.
In addition, in order to remove some of the oxygen which slips by the vacuum deareators and/or the gas-flushing apparatuses, it is sometimes desirable to add various chemical antioxidants to the beverage or food product. However, the consuming public is becoming much more concerned about the uses of chemicals and preservatives in foods and beverages including antioxidants, etc. Hence, it would be desirous to produce a process which removes oxygen from fluid streams without causing any harmful effects to the end product.
Moreover, the presence of oxygen in various industrial processes also produces a great deal of harm. In this regard, dissolved oxygen has been identified as a contributor in the corrosion of heating and cooling systems, such as boiler apparatuses and the primary and secondary coolant systems of nuclear power plants. It has been indicated that even low levels of dissolved oxygen (i.e. less than 20 parts of oxygen in one million parts of water) can contribute to the oxidation of the iron, copper, aluminum, brass, and other metallic components of these heating and cooling systems. The deoxygenation of water in fluids utilized in these systems is known to reduce corrosion and thereby extend equipment life, reduce pipeline and equipment costs, and lower overall maintenance.
Furthermore, it is also quite desirous to remove oxygen from various manufacturing processes. This is particularly true in a number of chemical processes, wherein the presence of oxygen can impede chemical reactions, as well as create undesirable side products. Similarly, in pharmaceutical processes, it is often quite beneficial to remove oxygenated compounds to avoid degradation, contamination, etc. Some of this technology is now being applied to new areas of research concerning biotechnology and semiconductor production where use of "ultra-pure" water is required.
Moreover, in various treatment processes, it is also advantageous to remove oxygen from the waste products in order to enhance anaerobic degradation. Anaerobic bacteria degradation systems are utilized in a wide variety of residential and industrial sewage treatment facilities. In addition, large manufacturers also utilize anaerobic bacteria degradation processes to break down various waste streams. In order to enhance the degradation of these waste products, it is important to maintain an overall anaerobic or deoxygenated state during the continuous on-line processing.
Accordingly, the present invention is directed to a continuous on-line apparatus and process for removing oxygen from various aqueous fluids in a safe and efficient manner without altering the desired properties of the products produced thereby. More particularly, the present invention is directed to the use of immobilized oxygen scavenging cell membrane fragments having an electron transport system which reduces oxygen to water. The membrane fragments contain a series of enzymes that work in cooperation with one another to convert the oxygen present in the fluids to water. By immobilizing the fragments, and in turn, immobilizing the effective enzyme system contained therein, it is possible to continuously remove oxygen from any process stream.
As a result, the present invention is substantially different from the previously known mechanical and chemical processes for removing oxygen from fluids. The only known reference which is similar to the present invention is the process disclosed in U.S. Pat. No. 4,414,334 for "Oxygen Scavenging With Enzymes", issued on Nov. 8, 1983 to Donald O. Hitzman of Bartlesville, Okla. In the '334 patent, the removal of ambient oxygen from aqueous liquids is catalyzed by alcohol oxidase in the presence of alcohol and optionally with catalase. While the process disclosed in the '334 patent has certain features in common with the present invention, i.e. the removal of oxygen enzymatically, the enzymes involved therein are distinctly different from the present invention in composition and effectiveness.
Specifically, the enzymes utilized in the process disclosed in the '334 patent are alcohol oxidase and catalase. These enzymes are extremely different from the enzymes contained in the membrane fragments of the present invention in structure, organization, and source. In this regard, the enzymes found in the cell membrane fragments of the present invention comprise a very intricate system, i.e. the electron transport system which reduces oxygen to water. These enzymes work in a cohesive relationship, and their location and arrangement in the membrane fragments is important to their proper and efficient function. Since the enzymes operate as a system within the membrane bound particles, the stability of the enzyme system is greatly enhanced.
In contrast, the enzymes in the '334 patent are individual proteins that are mixed together to give their desired reactions. These enzymes are not part of an integral system, but individual enzymes with only limited designation duty with no structural arrangement or association with one another.
Enzymes found in the cell membrane fragments of the present invention exist in all aerobic microorganisms, plants, and animals. However, the alcohol oxidase and catalase enzymes disclosed in the process of the '334 patent are often not found together in the same organism nor can they be isolated simultaneously. Furthermore, alcohol oxidase and catalase enzymes are not membrane bound.
Since the enzymes utilized in the '334 patent and the present invention differ greatly in composition and function, the methods for producing and/or isolating the enzymes are also very distinct. In this regard, one could not isolate the enzymes utilized in the present invention by the methods described in the '334 patent nor could one isolate the alcohol oxidase or the catalase utilized in the '334 patent by the methods described below.
Furthermore, the enzymes differ greatly in the substrates that they activate. The enzymes utilized in the present invention use a wide array of substrates as hydrogen donors, generally organic acids or their alkali salts. However, the enzymes utilized in the '334 process, i.e. alcohol oxidase and catalase react specifically with alcohols and hydrogen peroxide, respectively. Without the presence of either alcohol or hydrogen peroxide as the substrate, the enzymes utilized in the '334 patent would be inactive.
In addition, the enzymes of the present invention and the process disclosed in the '334 patent also differ in regard to the products produced. The enzymes utilized in the present invention often produce an organic acid and water as the end products, both of which are commonly found in biological materials, particularly food stuffs and thus, do not result in harmful additives. However, the alcohol oxidase utilized in the '334 patent produces an aldehyde and hydrogen peroxide as the end products. These end products are not widely found in nature and may not be desirable in food stuffs. Similarly, catalase utilized in the '334 patent reacts with hydrogen peroxide to produce oxygen and water. Thus, the '334 patent not only leads to the formation of undesirable products (aldehyde and hydrogen peroxide), it also results in the further production of oxygen, the product desired to be removed.
In summary, not only do the enzymes disclosed in the '334 patent differ from the enzymes utilized in the present invention in regard to composition and structure, the enzymes disclosed in the '334 patent are also inefficient in comparison to the enzymes of the present invention.